1. Field of the Invention
This invention relates to an ionic activity measuring device for quantitatively analyzing the activity or concentration of a specific ion contained in an aqueous liquid sample, for example, a wine, a beverage, service water, and in particular a body fluid (blood, urine, saliva or the like), by potentiometry.
2. Description of the Prior Art
As disclosed in, for example, Japanese Unexamined Patent Publication Nos. 58(1983)-211648, 59(1984)-30055 and 60(1985)-155960, there have been proposed slide type ionic activity measuring devices for receiving a liquid sample fed in drops and measuring the activity of a specific ion contained in the sample.
In the ionic activity measuring devices as disclosed in Japanese Unexamined Patent Publication Nos. 58(1983)-211648 and 60(1985)-155960, multiple sets of ion selective electrode pairs respectively having an ion selective layer selectively responding to a predetermined ion are provided as the outermost layer. The lower sections of the ion selective electrode pairs are secured to a lower supporting frame, and the upper sections thereof are covered by a water-impermeable member layer provided with liquid receiving through holes at the positions corresponding to the respective electrodes of the ion selective electrode pairs, at least one liquid receiving through hole being formed for each of the ion selective electrodes. By means of a pair of porous liquid distributing members formed of a cotton bandage cloth, a polyester mesh or the like are disposed on the waterimpermeable member layer so that each of the porous liquid distributing members makes each set of the liquid receiving through holes corresponding to the respective member electrodes of the ion selective electrode pairs, are communicated with each other. Also, an upper frame provided with a pair of liquid feed holes (i.e. liquid droplet holes) respectively communicating with the respective porous liquid distributing members is disposed on the pair of porous liquid distributing members to match the lower supporting frame. A porous bridge formed of twisted fiber yarn or the like for achieving liquid junction, thus electrical conduction, between a sample solution fed in drops to one of the pair of the liquid droplet holes and a reference solution fed in drops to the other thereof is disposed, usually, on the pper frame.
In the case where the ionic activity measuring device having the aforesaid configuration is provided with, for example, multiple sets of the ion selective electrode pairs responding respectively to Na.sup.+, K.sup.+, and Cl.sup.- ions, drops of a reference solution having known activity values of these ions are fed to one of the pair of the liquid droplet holes, and drops of a sample solution wherein the activity values of these ions are unknown are fed to the other of the pair of the liquid droplet holes. The reference solution and the sample solution penetrate through the porous liquid distributing members to the corresponding ion selective electrodes via the liquid receiving holes. On the other hand, the reference solution and the sample solution contact each other to achieve a liquid-junction near the middle of the porous bridge (hereinafter often referred to simply as the bridge), and electrical conduction is effected between the two solutions. As a result, a potential difference proportional to the difference in activity of each ion between the reference solution and the sample solution arises between the electrodes of each ion selective electrode pair. By measurement of the potential differences, the activity values of the Na.sup.+, K.sup.+, and Cl.sup.- ions contained in the sample solution can be determined simultaneously or sequentially based on the measured values and calibration curves determined in advance from the activity values of the ions in the standard solution (by use of the Nernst equation).
With the aforesaid ionic activity measuring device, it is possible to measure the ionic activity values of a plurality of ions simply by feeding drops of the sample solution and the reference solution just once. Therefore, the ionic activity measuring device is very advantageous for analysis of an aqueous liquid sample, particularly for clinical analysis of a sample such as blood taken from the human body.
In the conventional ionic activity measuring device, the porous bridge is normally disposed on the upper surface of the upper frame in the vicinity of the liquid feed holes. Therefore, when a plurality of the ionic activity measuring devices are stacked and subjected to packaging, inspection or operation for measurement, the porous bridge of the ionic activity measuring device is often damaged or removed by the edges of the adjacent ionic activity measuring device placed on the upper side. The porous bridge is also readily damaged by a liquid feed instrument such as a pipette.
The primary object of the present invention is to provide an ionic activity measuring device wherein the time taken for a sample solution or a reference solution to arrive at the electrode surfaces is short so that the time required for ionic activity measurement is shortened, adverse effects of hemolysis of a whole blood sample solution are eliminated, and ionic activity measurement is not adversely affected by bubbles generated when a fed solution contacts the porous liquid distributing members.
Another object of the present invention is to provide an ionic activity measuring device wherein a sample solution and a reference solution fed in drops from liquid feed holes are allowed to smoothly permeate through porous liquid distributing members and quickly arrive at ion selective electrode pairs, and the solutions are fed reliably to the surfaces of ion selective electrodes by eliminating air confinement.
The specific object of the present invention is to provide an ionic activity measuring device which eliminates adverse effects of hemolysis of a whole blood sample solution and accurately measures ionic activity of the K.sup.+ ion (potassium ion).
The present invention provides an ionic activity measuring device comprising:
(i) at least one pair of sheet-like ion selective electrodes provided with ion selective layers on their surfaces and electrically isolated from each other,
(ii) at least one pair of porous liquid distributing members for feeding a reference solution and a sample solution respectively to said ion selective layers of said ion selective electrodes,
(iii) a frame for housing said ion selective electrodes and/or said porous liquid distributing members therein and provided with a pair of liquid feed holes respectively disposed above said porous liquid distributing members for feeding said reference solution and said sample solution independently of each other to said porous liquid distributing members, and
(iv) a porous bridge for achieving electrical conduction between said reference solution and said sample solution fed to said pair of the liquid feed holes,
wherein the improvement comprises disposing said porous bridge in a recess formed in the upper surface of said frame, and adjusting the depth of said recess to a value not smaller than the height of said porous bridge.
With the ionic activity measuring device in accordance with the present invention, wherein the porous bridge does not project above the surface of the frame, another measuring device, a pipette or the like does not readily come into contact with the bridge. Therefore, it is possible to prevent the bridge from being damaged or removed, and to efficiently measure ionic activity.
The present invention also provides an ionic activity measuring device comprising the aforesaid members (i) to (iv), wherein the improvement comprises protruding an end portion of at least either one of said porous liquid distributing members to a part of a region under the corresponding liquid feed hole, whereby said reference solution or said sample solution is allowed to enter from the side face of said end portion.
With the second mentioned ionic activity measuring device in accordance with the present invention, wherein at least either one of the porous liquid distributing members is protruded to the region under the corresponding liquid feed hole, it is possible to prevent hemolysis of a whole blood sample solution and to eliminate bubbles contained in a fed solution. This device is suitable particularly for ionic activity measurement of whole blood.
In the second mentioned ionic activity measuring device in accordance with the present invention, "protruding" and "facing" embrace also the case where the liquid feed hole and the porous liquid distributing member meet each other only at a part of the side face of the end portion of the porous liquid distributing member. The shape of the end portion of the porous liquid distributing member (the shape on a projected plane as viewed normal to the liquid distribution advance direction) is not limited, and may be a linear shape, a circular arc shape (convex or concave), a curvilinear shape, or a shape constituting a part of a polygon (e.g. a hexagon or a octagon).
Also, end portions of two or more porous liquid distributing members may be disposed to face the region under the corresponding liquid feed hole.
In the case where the porous liquid distributing members are formed of a woven fabric or a knitted fabric having comparatively small interstices, for example, a cotton bandage cloth, cotton gauze, PET gauze or a cotton tricot, or a non-woven fabric or filter paper having small continuous pores and constituted by cotton fiber, regenerated cellulose fiber or synthetic polymer fiber, it takes a comparatively long time for a sample solution of relatively high viscosity to penetrate through the porous liquid distributing members when the sample solution is fed normal to the longitudinal direction of the fiber. Therefore, the configuration of the second mentioned ionic activity measuring device in accordance with the present invention, wherein the solution is fed mainly from cut ends of fibers of the porous liquid distributing members, is particularly advantageous for the porous liquid distributing members having small interstices or small continuous pores.
The liquid feed holes may be of any shape, such as a circle having a diameter within the range of approximately 1.5 mm to approximately 8 mm, or an ellipse or a polygon inscribed in the circle. When a plurality of the porous liquid distributing members are provided to face the corresponding liquid feed hole, they are spaced from each other at a distance within the range of approximately 1 mm to approximately 6 mm, preferably within the range of approximately 2 mm to approximately 3 mm, in the liquid distributing direction.
The present invention further provides an ionic activity measuring device comprising the aforesaid members (i) to (iv), wherein the improvement comprises extending said porous bridge through said pair of the liquid feed holes at positions deviated from centers of said liquid feed holes.
With the third mentioned ionic activity measuring device in accordance with the present invention, since the porous bridge is deviated from the centers of the liquid feed holes, drops of a reference solution or a sample solution may be fed to the center of each liquid feed hole so that the drop of liquid does not directly fall onto the porous bridge. Therefore, it is possible to eliminate loss of the solution caused by liquid repulsing by the bridge, and to prevent the bridge from being damaged by contact with an end of a pipette. As a result, it becomes possible to measure ionic activity accurately, quickly and easily.
The present invention also provides an ionic activity measuring device comprising:
(i) at least one ion selective electrode pair composed of solid-state electrodes provided on their surfaces with ion selective layers selectively responding to a predetermined ion, PA1 (ii) at least one pair of liquid distributing members for feeding a reference solution and a sample solution respectively to said ion selective layers of said ion selective electrode pair, PA1 (iii) a frame for supporting therein said ion selective electrode pair and said liquid distributing members and provided with a pair of liquid feed holes for feeding said reference solution and said sample solution independently of each other to said liquid distributing members, and PA1 (iv) a bridge for achieving electrical conduction between said reference solution and said sample solution fed to said pair of the liquid feed holes, PA1 (i) at least three pairs of sheet-like ion selective electrodes provided with ion selective layers on their surfaces and electrically isolated from each other, PA1 (ii) at least one pair of porous liquid distributing members for feeding a reference solution and a sample solution respectively to said ion selective layers of said ion selective electrodes, PA1 (iii) a frame for housing said ion selective electrodes and said porous liquid distributing members therein and provided with a pair of liquid feed holes respectively disposed above said porous liquid distributing members for feeding said reference solution and said sample solution independently of each other to said porous liquid distributing members, and PA1 (iv) a porous bridge for achieving electrical conduction between said reference solution and said sample solution fed to said pair of the liquid feed holes,
wherein the improvement comprises providing said frame with potential measurement holes for allowing potential measuring probes to be inserted therethrough from the exterior to contact terminal sections of said ion selective electrode pair.
With the fourth mentioned ionic activity measuring device in accordance with the present invention, wherein the ion selective electrode pair is supported inside of the frame and the frame is provided with the potential measurement holes (i.e. through holes for insertion of potential measuring probes) communicating with the exterior, potential measurement can be conducted by inserting potential measuring probes from the exterior into the holes until the probes contact terminal sections of the ion selective electrode pair, and therefore it is possible to strengthen supporting of the terminal sections of the ion selective electrode pair and to prevent the ion selective electrode pair from being bent or damaged. Also, since the frame need not be partly cutaway for exposing the terminal sections of the ion selective electrode pair, it is possible to increase the strength of the frame, and consequently the strength of the ionic activity measuring device.
The present invention further provides an ionic activity measuring device comprising the members (i) to (iv) just mentioned above, wherein the improvement comprises providing a supporting section of said frame, where said frame supports said liquid distributing members, with air discharging holes for making said supporting section of said frame for said liquid distributing members communicating with the exterior at positions spaced from said liquid feed holes.
With the fifth mentioned ionic activity measuring device in accordance with the present invention, the air discharging holes are formed for making the supporting section of the frame for the liquid distributing members communicating with the exterior at positions of said supporting section remote from the liquid feed holes. Therefore, when a reference solution and a sample solution are independently fed from the liquid feed holes to the liquid distributing members, air in the liquid distributing members is pushed by the solutions and discharged through the air discharging holes to the exterior, so that the solutions smoothly permeate through the liquid distributing members. Accordingly, the solutions arrive quickly at the ion selective electrode pair without bubbles remaining midway along the liquid distributing members, and it becomes possible to conduct potential measurement quickly.
The present invention also provides an ionic activity measuring device comprising:
said at least three pairs of the sheet-like ion selective electrodes being disposed to stand side by side along said porous liquid distributing members, and said pair of the liquid feed holes being disposed in the vicinity of the center between the ion selective electrode pair positioned at one end and the ion selective electrode pair adjacent to said ion selective electrode pair positioned at said end,
wherein the improvement comprises constituting said ion selective electrode pair adjacent to said ion selective electrode pair positioned at said one end, by a pair of potassium ion selective electrodes.
With the sixth mentioned ionic activity measuring device in accordance with the present invention, it is possible to prevent hemolysis of a whole blood sample solution and to accurately measure ionic activity of a potassium ion contained in the whole blood. In this ionic activity measuring device, the porous liquid distributing members are preferably disposed so that an end portion of at least one of the members faces the corresponding liquid feed hole as mentioned above with reference to the second mentioned ionic activity measuring device in accordance with the present invention.